In recent years, for example, in a storage device used in a mainframe, many logical volumes are included in the physical volume since a capacity of a physical volume becomes larger than a size of a logical volume. The logical volume is a logical storage area in which an application stores data, and the physical volume is a physical storage area of a nonvolatile storage device which actually stores the data.
Since input and output (I/O) processing between a host and the storage device is parallelized, writing of the data to the plurality of logical volumes is performed in parallel. The host is an information processing device on which the application operates.
FIG. 8 is a diagram illustrating an example of writing the data from the host to the logical volume. As illustrated in FIG. 8, the host 2 may perform four writes in parallel through four channels 21 represented by a CH #0 to a CH #3.
A storage device 9 accepts a write request by using a CA # A to a CA # D respectively associated with the CH #0 to the CH #3. The CA # A to CA # D are channel adapters (CA) 11. The CA # A to CA # D pass the received write request to a controller module (CM) 91.
The CM 91 controls the storage device 9, and writes the data written in the storage device 9 by the host 2 into a RAID group logical unit (RLU) 92 represented by an RLU #0 to an RLU #3. The RLU 92 has two physical volumes 41, mirrors the data written in the storage device 9 by the host 2, and stores the data in two logical volumes 42. The two logical volumes 42 are placed in separate physical volumes 41.
The CM 91 has a cache memory 31, a cache control unit 93, and a least recently used (LRU) table 33. The cache memory 31 temporarily stores the data to be written to the RLU 92 and the data read from the RLU 92 on a cache page basis. The cache memory 31 stores the data to be written in the RLU 92 as dirty data 31a. 
The cache control unit 93 controls writing of the data and reading of the data by using the cache memory 31. When the cache memory 31 is exhausted, the cache control unit 93 releases the cache memory 31 on a cache page basis based on the LRU table 33.
The LRU table 33 stores information of cache pages in the order in which the cache pages are not used. When the cache memory 31 is exhausted, the cache control unit 93 takes out information of the cache page from a head of the LRU table 33 and releases the cache page. At this time, the dirty data 31a, for example, the cache page which became dirty after being written, is written back to the RLU 92.
As a technology relating to mirroring in related art, there is a technology for generating an optimum mirror server group according to an access load situation on an origin server by adapting any node in a network as a mirror server. In the technology, when the origin server performs dynamic mirroring of content, an adaptive mirror node detecting unit detects an adaptive mirror node in the network, and a dynamic mirror destination determining unit selects the adaptive mirror node of a mirror destination. A dynamic mirror request unit performs a dynamic mirror request to the selected adaptive mirror node, and when the request is accepted, the mirror content is transferred by a dynamic mirror unit. The adaptive mirror node stores the received mirror content in a mirror content storage unit and functions as the mirror server.
There is a dynamic load balancing storage method which reduces delay of a response when a load concentrates on a certain hard disk drive, which is not predicted beforehand, and reduces degradation of a service. The dynamic load balancing storage method monitors a degree of load concentration on each hard disk drive and copies content of a detected overload hard disk drive to a mirror hard disk drive. In the dynamic load balancing storage method, part of an access request to the overload hard disk drive is regarded as an access request to the mirror hard disk drive, and access is executed.
There is a technology in related art in which reading performance from a table is enhanced by acquiring an access instruction accessing a database, predicting the table to be accessed in accordance with the acquired access instruction, and mirroring the predicted table among a plurality of storage devices.
For example, Japanese Laid-open Patent Publication Nos. 2006-146951, 2007-310715, and 2012-137870 discuss the above related technologies.